wasm codegen: fix mistaking extern data as function

src/InternPool.zig

@@ -616,6 +616,20 @@ pub const Nav = struct {
         };
     }
 
+    pub fn isFn(nav: Nav, ip: *const InternPool) bool {
+        return switch (nav.status) {
+            .unresolved => unreachable,
+            .type_resolved => |r| {
+                const tag = ip.zigTypeTagOrPoison(r.type) catch unreachable;
+                return tag == .@"fn";
+            },
+            .fully_resolved => |r| {
+                const tag = ip.zigTypeTagOrPoison(ip.typeOf(r.val)) catch unreachable;
+                return tag == .@"fn";
+            },
+        };
+    }
+
     /// If this returns `true`, then a pointer to this `Nav` might actually be encoded as a pointer
     /// to some other `Nav` due to an extern definition or extern alias (see #21027).
     /// This query is valid on `Nav`s for whom only the type is resolved.

src/arch/wasm/CodeGen.zig

@@ -1022,7 +1022,7 @@ fn emitWValue(cg: *CodeGen, value: WValue) InnerError!void {
             const comp = wasm.base.comp;
             const zcu = comp.zcu.?;
             const ip = &zcu.intern_pool;
-            if (ip.getNav(nav_ref.nav_index).isExternOrFn(ip)) {
+            if (ip.getNav(nav_ref.nav_index).isFn(ip)) {
                 assert(nav_ref.offset == 0);
                 const gop = try wasm.zcu_indirect_function_set.getOrPut(comp.gpa, nav_ref.nav_index);
                 if (!gop.found_existing) gop.value_ptr.* = {};